PARENT SESSION
Oral Session #51: Invasions: Population and community interactions.
Presiding: T. Stohlgren
Wednesday, August 7. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.

Invasiveness of Ammophila arenaria: Release from soil-borne pathogens?

BECKSTEAD, JULIE^*,1, PARKER, INGRID¹, ¹ University of California, Santa Cruz, Santa Cruz, CA

ABSTRACT- The Natural Enemies Hypothesis (i.e., invading species are free from their natural enemies) is a common explanation given to explain why invasive species are so successful. We tested this hypothesis for an invasive species, Ammophila arenaria (European Beachgrass), which invades the coastal dunes of California. European research on Ammophila in its native range has established that soil-borne pathogens, primarily nematodes and fungi, reduce Ammophila's growth. In a greenhouse experiment designed to parallel European studies, seeds and two-week old seedlings were planted in sterilized (free of pathogens) and non-sterilized (field-collected soil from Ammophila root zone) soil. We found that soil-borne pathogens, primarily fungi, reduced seed germination by 15%, increased seedling mortality by 17%, and reduced plant biomass of individuals by 70%. Similarly, European studies showed a 77% reduction in plant biomass for Ammophila grown in non-sterilized soil containing pathogens compared with sterilized soil. These data indicate that Ammophila is subjected to similar pathogenic pressures in its introduced range in comparison to its home range. Although European studies found that both pathogenic nematodes and fungi reduce Ammophila's growth, we found that pathogenic nematodes were functionally absent in this study. Although the release from enemies is frequently cited as an explanation for the invasive nature of invasive species, we found that a release from soil-borne pathogens does not explain the invasion success of Ammophila in its introduced range.

KEY WORDS: natural enemies hypothesis, plant pathogen interactions, invasion biology